Burners heretofore used for producing a flat flame over a wide area include a relatively elongated flaring section extending from the mixing chamber to the combustion chamber so as to permit thoroughly mixed fuel and air to flow into the combustion chamber and spread out in radial directions. With such structure, the flame may spread out radially to some extent, but because of provision of the elongated flaring opening, the axial component of jet velocity exerts influence on the flame to result in increase in the overall thickness of the flame in the axial direction of the egressed flame. Thus, the burner of the above-mentioned type fails to provide a flat flame.
Furthermore, the burner which includes a flaring section such as above, requires an elongated construction and the necessity to employ a refractory structure made of bricks or the like adds to the thickness of the constituent wall portions at the sacrifice of effective work space and renders the overall structure heavier.